This application claims the priority benefit of Taiwan application serial no. 89127333, filed Dec. 20, 2000.
1. Field of Invention
The present invention relates to a power converter. More particularly, the present invention relates to a power converter with adjustable output voltage.
2. Description of Related Art
With the refinement of semiconductor fabrication technologies, the operating voltage of most semiconductor devices has dropped considerably. In the past, a constant voltage such as 12V, 5V or 3.3V was applied to most semiconductor devices. At present, the operating voltage of most semiconductor devices is smaller than 3.3V. In addition, the operating voltage no longer has to be fixed at a definite value. For example, to obtain a higher operating efficiency, a central processing unit (CPU) communicating with a chipset, memory units or other devices can adjust the operating voltage automatically. In other words, the power supply must be able to provide an output voltage that can be adjusted automatically.
In the design of most power converters, a monolithic integrated circuit (monolithic IC) is often used to perform pulse width modulation (PWM). FIG. 1 is a diagram showing a conventional power converter 10 and a portion of its internal electric circuit. To control pulse width, a voltage comparator 110 is used inside a pulse width modulation IC (PWM IC). The voltage comparator 110 compares the output voltage +V0 of the power converter 10 with a reference voltage Vref. To program the output voltage of the power converter 10, the semiconductor manufacturer incorporates a digital-to-analog (D/A) converter 120 inside the PWM IC 100. According to the input digital signals such as VID0, VID1, VID2 . . . VIDn, the digital/analog converter 120 determines the output reference voltage Vref. The digital signals VID0, VID1, VID2 . . . VIDn are called the voltage identification codes.
By setting the bit values of the voltage identification codes VID0, VID1, VID2 . . . VIDn, quantity of the output voltage can be varied. Using a 5bit voltage identification code as an example, all the voltage identification codes VID0xcx9cVID4 having a bit value xe2x80x981xe2x80x99 may imply an output voltage of 0V. On the other hand, all the voltage identification codes VID0xcx9cVID4 having a bit value xe2x80x980xe2x80x99 may imply an output voltage of 1.85V. A change in any one bit value may represent an ultimate difference in the output voltage of about 0.025V. Hence, by setting the voltage identification codes VID0xcx9cVID4, the output voltage provided by the power converter may be changed accordingly. The process of finding the relationship between a bit arrangement of the voltage identification codes and corresponding output voltage is often referred to as a bit mapping.
Since semiconductor fabrication involves a large number of processes, each device may be affected by many variables. Hence, for different semiconductor devices, different operating voltages are required. To provide different operating voltages, a power converter having different voltage identification codes in the PWM IC must be used. However, designing the voltage identification codes in a PWM IC often take more than a year. In a rapidly changing semiconductor marketplace, such a slow turnover rate is unacceptable.
Accordingly, one object of the present invention is to provide an adjustable output voltage power converter that permits fine tuning of the voltage produced by a pulse width modulation integrated circuit with any kind of voltage identification codes, so that the same type of power converter can be used to provide a range of operating voltages.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an adjustable output voltage power converter. The power converter includes a voltage comparator, a voltage shift resistor and a current source. The voltage comparator has two input terminals and a compare output. The compare output of the voltage comparator is electrically coupled to one end of a Zf One of the input terminals of the voltage comparator is electrically coupled to the other terminal of the Zf and one end of a Zi. The other end of the Zi is electrically connected to the current source and the other terminal of the voltage shift resistor. The other terminal of the voltage shift resistor is electrically coupled to a positive voltage output terminal. In addition, the other input terminal of the voltage comparator receives a reference voltage to serve as a reference for voltage comparison.
The reference voltage can be provided by a digital-to-analog converter. The digital-to-analog converter receives a voltage identification code that includes a set of inputs and produces a reference voltage that corresponds to the voltage identification code.
In this invention, the voltage-regulating circuit that includes the current source and the voltage shift resistor can be electrically coupled to the negative voltage output terminal of the power converter. By adjusting voltage at the negative voltage output terminal, output voltage of the power converter can be adjusted.
In another aspect of this invention, the positive voltage output terminal and the negative voltage output terminal are electrically coupled via the current source. Furthermore, a voltage shift resistor is coupled to the circuit path between the current source and the positive voltage output terminal. Similarly, another voltage shift resistor is coupled to the circuit path between the current source and the negative voltage output terminal. With such an arrangement, the current source is able to adjust voltage at both the positive and the negative voltage output terminal concurrently so that a small current can be used to obtain identical voltage variation.
This invention also provides an alternative type of adjustable output voltage power converter. The power converter includes a positive voltage output terminal, a negative voltage output terminal and a pulse width modulation integrated circuit (PWM IC). According to a voltage identification code, the PWM IC outputs a corresponding adjustable voltage to the positive voltage output terminal via a Zi. The power converter further includes a voltage shift resistor and a current source. In one of the embodiments of this invention, one of the terminals of the voltage shift resistor is electrically coupled to the Zi while the other terminal of the voltage shift resistor is electrically coupled to the positive voltage output terminal. One terminal of the current source is electrically coupled to the circuit path between the voltage shift resistor and the Zi.
According to a second embodiment of this invention, one terminal of the voltage shift resistor is electrically coupled to the negative output terminal while the other terminal of the voltage shift resistor is electrically coupled to the negative voltage output terminal. One terminal of the current source is electrically coupled to the circuit path between the voltage shift resistor and the negative output terminal.
According to a third embodiment of this invention, altogether two voltage shift resistors and a current source are used. One terminal of the first voltage shift resistor is electrically coupled to the Zi while the other terminal of the first voltage shift resistor is electrically coupled to the positive voltage output terminal. One terminal of the second voltage shift resistor is electrically coupled to the negative output terminal while the other terminal of the second voltage shift resistor is electrically coupled to negative voltage output terminal. One terminal of the current source is electrically coupled to a circuit path between the Zi and the first voltage shift resistor. Similarly, the other terminal of the current source is electrically coupled to a circuit path between the negative output terminal and the second voltage shift resistor.
In brief, the voltage-adjustable circuit constructed using a current source and a voltage shift resistor is set up to modify the voltage range of a power converter. Hence, there is no need to design a PWM integrated circuit anew for a different voltage identification code.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.